Adhesive laminates including a layer of a normally tacky, pressure sensitive adhesive adhered to at least one surface of a supporting web (or facing layer) are typically cut to size during one or more operations in their manufacture. A plurality of laminate sheets comprising such supporting web (or facing layer) and pressure sensitive adhesive adhered thereto are stacked and cut to the desired size by means of a knife blade, commonly known as a guillotine.
During cutting, pressure sensitive adhesive has the tendency to flow at the cutting edge, either because of its inherent flowability or a combination of that at flowability and the exertion of pressure shear force by the cutting blade. As a result of the adhesive flow, the cutting blade tends to become coated with a layer of the adhesive. This coating tends to reduce the efficiency of further shearing cuts, to limit markedly the number of laminate sheets which can be cut with a single stroke of the cutting blade, and to deposit and smear adhesive on the edge surfaces of the articles being cut.
Acrylic polymers are known for their suitability for outdoor uses. Moreover, water based acrylic adhesives (i.e. acrylic emulsion adhesives) are well known. Certain water based acrylic adhesives are permanent adhesives, that is, they have a high ultimate adhesion value for various substrates, so that when such adhesive is used to join a label to a substrate (such as a shipping drum or carton), the label cannot be removed without destroying the label, and frequently there is some damage to the substrate as well. The properties of high outdoor suitability and permanency make permanent acrylic adhesives an ideal candidate for shipping labels. In fact, such acrylic adhesives are used for this purpose. However, adhesive labels are invariably desired in a smaller size than the size of the adhesive laminate sheets as initially prepared. This requires cutting to size. This is done economically by stacking a large number of sheets and cutting with a knife blade or guillotine. The problem that arises is the aforedescribed edge flow, which coats the knife blade, smears the laminate and in a short time renders the cutting operation less efficient.
U.S. Pat. No. 4,346,189 to Laurent describes solvent based pressure sensitive adhesive compositions comprising synthetic rubber, tackifiers and about 6 to 10 percent by weight (based on total dry composition weight) of a silicone additive. The silicone additive is a low molecular weight polysiloxane having a maximum weight average molecular weight of about 11,000. This additive improves properties of the adhesive composition so that virtually no adhesive oozes out at the edge when a stack of laminates containing this composition is cut. The polysiloxane additives successfully solves the problem of edge flow in the synthetic rubber adhesive compositions disclosed therein. However, synthetic rubber adhesives are not suitable for certain purposes, such as labeling of corrugated drums and other shipping cartons, because the adhesive may lack the specific adhesion to corrugated board and fiber drums which is required for shipping labels, may show inadequate ultimate adhesion that is required in a permanent adhesive, and does not provide long term outdoor aging or durability.
Published European Patent Application No. 0 126 312 describes pressure sensitive adhesive compositions and laminates in which improved cutting properties are obtained by adding a polyoxyalkylene polyol such as polyethylene glycol to a mixture which includes a water soluble elastomeric polymer and a tackifier. The solvent base and aqueous emulsion base elastomeric polymers are disclosed; the latter include emulsified acrylic resins. A problem with such adhesive compositions is that polyoxyalkylene glycols are rather hydrophilic so that the resulting adhesive composition is not as water proof as one would desire in an adhesive to be used in shipping carton labels.
U.S. Pat. No. 4,151,319 to Sackoff et al discloses pressure sensitive adhesive compositions and laminates having low "zero minute peel value" (initial adhesion). Among the adhesives disclosed are water based acrylic adhesives containing from about 0.001 to 20 percent by weight (dry basis), preferably from about 0.1 to 1.0 percent by weight, based on polymer solids, of a polysiloxane additive which reduces zero minute peel value. The polysiloxane additive may be either a dimethylsiloxane-oxyalkylene block copolymer, or a more hydrophobic, high molecular weight polysiloxane such as a polydimethylsiloxane. Because of the low initial adhesion or "zero minute peel value" of the adhesive compositions in this patent, it would be necessary to hold a laminate containing such adhesive against a substrate for a while in order to obtain adhesive bonding. This, of course, is unacceptable in adhesives for use as labels, since the user wishes to apply the adhesive label to the substrate as fast as possible and have it stick.
While the problem of edge ooze in solvent based synthetic rubber adhesives has been solved, it has not been solved in water based acylic adhesives. The present invention offers a solution to this problem.